There are many applications where it is necessary to spray a fluid material onto a surface, often the ground. This application is most notable in agriculture, horticulture and such things as golf course maintenance and pest control where chemicals are mixed with water and then sprayed on the ground, bodies of water or on growing crops. Various fluids must also often be sprayed on roadways and other surfaces as well.
Spraying is accomplished with ground sprayers, either self-propelled or towed units, and with aerial sprayers mounted on airplanes or helicopters.
Such sprayers commonly comprise a tank of fluid, a pump for pressurizing and distributing the fluid to spray nozzles and means to control the fluid pressure. Sprayers typically have a plurality of nozzle bodies, each securing a spray nozzle, mounted on booms which swing in for transport and out for operation. Airplane mounted sprayers typically have a boom fixed to the wings.
The nozzle locations are spaced apart on a boom, perpendicular to the direction of travel, at a standard spacing distance which corresponds to the spray pattern of the nozzles. The same size nozzle is in operating position at each nozzle location, providing a consistent application rate across the width of the sprayer. The most common spray pattern is a flat-fan pattern, and the nozzles are generally rotated approximately 10 degrees from being perpendicular to the direction of travel in order that the overlapping spray patterns do not intersect and interfere with each other.
The booms may be of the "wet boom" type, where the boom comprises a frame member with a pipe mounted thereon, the fluid passing through the pipe into nozzles mounted on the pipe and fluidly connected thereto, or a "dry boom" type, where the nozzles are mounted to the frame member and fluid passes to the nozzles through a hose which is connected between the nozzles. The "boom" then is the structure upon which the nozzles are mounted, fluid passing directly through the "wet boom", and fluid passing through a separate hose to nozzles mounted on a "dry boom".
A pump delivers the fluid to the nozzles, the fluid pressure being controlled by a pressure regulating valve.
Such sprayers must accurately dispense the fluid over the desired area of ground. Historically this has been accomplished by providing a spray nozzle having a set operating pressure such that when operated at that pressure, the nozzle accurately dispensed a known amount of fluid per time unit. Operating the sprayer at a known speed then accurately resulted in the correct amount of fluid being dispensed over a given area. For example a sprayer nozzle designated 01 would apply 22 liters per acre of ground covered when operated at a pressure of 40 pounds per square inch (psi) and a speed of 5 mph. A nozzle designated 02 would apply 45 liters per acre at the same pressure and speed.
At pressures above or below the operating pressure of 40 psi, the spray pattern would distort, and the proper amount of fluid would not be accurately distributed across the width of the spray pattern.
One obvious problem was that as speed increased or decreased the application rate increased or decreased accordingly. To help overcome this problem, "extended range" nozzles were developed which maintained an accurate distribution across the width of the spray pattern at a range of pressures from approximately 20 psi to 60 psi. If the operator wanted to spray at an increased speed, he could increase the pressure to maintain the same application rate, and similarly the pressure could be reduced if he wanted to reduce his speed. Rate controllers became available as well which measured the total flow of fluid to the nozzles and automatically varied the pressure as the speed varied, maintaining a constant total flow to the nozzles and therefore a stable application rate. Using, for example an ER01 nozzle, the operator could maintain a 22 liter per acre application rate while traveling from approximately 3.5 mph to 6 mph.
Such extended range nozzles also facilitated variations in the application rate if desired. Using the ER01 nozzles again, at a speed of 5 mph, the operator could vary the application rate from approximately 16 liters per acre to 27 liters per acre.
In order to exceed these application rates, or to exceed these speeds, a nozzle change is required. Various systems are available whereby three or more different nozzles are located on a swivel at each nozzle location. Only one of these nozzles is in the operating position at any given time, and to change to a different nozzle, the operator is required to stop and manually rotate the swivel to put a different nozzle into the operating position
Application rates required for ground sprayers range from 12 liters per acre to 250 liters per acre. Speeds range from 4 mph to in excess of 25 mph. Many custom applicators encounter a wide range of application rates every day, requiring frequent nozzle changes daily, and costly delays. As well, operators often have difficulty maintaining the sprayer speed within the required range. Often rough ground is encountered, or corners, requiring much reduced speed.
Aerial sprayers travel much faster, however similar limitations apply as to the variability of application rates. The object is to apply a given amount of material on a given area.
Sprayers are presently available which have two booms. There are two separate pumps and two separate tanks typically containing two different fluids. A different fluid is delivered to each boom and the nozzles mounted thereon. The booms may be operated independently, allowing for different fluids to be applied on different areas as the sprayer passes over them. Essentially there are two separate sprayers carried on the same frame. Alternatively, the same fluid could be contained in each tank, or a single pump and tank could deliver fluid to each boom. With one size nozzle operating on one boom, and a different size nozzle operating on the second boom, a wider range of application rates could be obtained than is possible with one nozzle.
While a dual boom sprayer could provide the same benefits as two sets of nozzles on the same boom, the very high cost of such sprayers has made them economically feasible only where the application of two separate fluids makes an extra trip over the ground unnecessary. The cost of having three booms to provide a system with increased versatility would be prohibitive.